1. Field of the Invention
The present invention relates to an encoded data modification device, a modification method, and a modification program that are capable of embedding electronic watermarks with small delays, in which, in embedding an electronic watermark in, e.g., MPEG-encoded video data without decoding the video data, judging means is provided to judge whether the data can be modified within a predetermined delay.
2. Description of the Related Art
Recently, a need to modify already encoded data has been arising because of, e.g., demands to prevent illegal copies by adding a unique code to the content in network distribution of video signal. In such a process, modifying the video signal itself according to predetermined rules to convert the total content into a different form is called fingerprinting or electronic watermarking, which is more secure than techniques in which some information is simply written in headers. When the process is performed during a distribution of content, a technique is desired which adds the target modification with the least decoding of the encoded data. In such a case, when the encoded data is transmitted at a given rate, the amount of code, after modified, should not be increased because it may result in overflow of decoder buffers.
There are several conventional methods that prevent an increase in the amount of code. For example, a method is disclosed in which data is left unmodified when the amount of code is increased (for example, see F Hartung and B. Girod, “Digital Watermarking of MPEG-2 Coded Video in the Bitstream Domain,” Proceedings of International Conference on Omge Processing, 1997). Also, another method is disclosed in which, after modification, the absolute values of DCT coefficients are decreased until the increase in the mount of code is eliminated (for example, see A. M. Allattar, E. T. Lin, and M. U. Celik, “Digital Watermarking of Low Bit-Rate Advanced Simple Profile MPEG-4 Compressed Video,” IEEE Transactions on Circuits and Systems for Video Technology, vol. 13 no. 8, 00. 787-800, August 2003.).
The conventional methods detect whether modification of a signal increases the amount of code, and inhibit the modification or reduce other information in the case of an increase of the amount of code so as to finally avoid the increase. However, because data is variable-length encoded, a modification of one signal may affect the encoded data to varying extents. This causes a need to provide a memory capable of storing the largest possible amount, leading to a problem of large signal delays.